The aim of the study is to investigate the cholinergic deficit in Alzheimer's disease (AD) and identify candidate blood biomarkers for the diagnosis of the disease. Twenty-nine elderly Chinese diagnosed with AD and 33 age-matched controls were selected. The activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in plasma were detected by a spectrophotometric method, and the mRNA levels of alpha4 and beta2 nicotinic acetylcholine receptor (nAChR) subunits in blood leukocytes were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). The results showed that AChE activity in plasma was significantly lower in the AD group than in normal controls, while BuChE activity did not show any differences between AD and controls; mRNA levels of both alpha4 and beta2 nAChR subunits in blood leukocytes were significantly lower in the AD group than in controls. The AChE activity and the mRNA levels of alpha4 and beta2 nAChR subunits in the AD patients were also significantly correlated with cognitive test scores. No differences of AChE in plasma or alpha4 and beta2 nAChR subunits in blood leukocytes were detected between smoking and non-smoking subjects. The results indicated that the decreases in the activity of AChE and in the mRNA levels of nAChR alpha4 and beta2 subunits from the peripheral blood of patients with AD might serve as supplementary indicators for the clinical diagnosis of AD.